Tales of brave Ulysses

The Ulysses sun-orbiting spacecraft has become the Bret Farve of robotic solar-system explorers.

After an illustrious career, it was about to fizzle out retire, then it defied the pundits and played another season.

Well, the project's officials announced today that they will pull the plug on Ulysses at the end of this month. Not bad for a space probe whose imminent "retirement" was to have occurred early last year.

The craft -- a cooperative project between the European Space Agency and the National Aeronautics and Space Administration -- has spent the last 18.5 years orbiting the sun over its poles, giving solar physicists a unique perspective on how the sun's magnetic fields and energetic particles it ejects move through the solar system.

Here on Earth, we call it space weather. ESA has a nice summary of Ulysses's contributions to understanding space weather on its web site.

In February 2008, mission engineers announced with great solemnity and with heaps of praise for the orbiter that the craft would fall silent within a few months. Its power supply had grown too weak to keep the craft's fuel lines from freezing. Not so fast: Engineers figured out that they could keep the lines warm by firing the craft's thrusters in short bursts every couple of hours.

Now, however, the craft is moving away from Earth in its solar orbit. It's no longer able to send data at a speedy enough rate to merit yet another "season" on the active roster.

So, on June 30, ground controllers will order Ulysses to silence its transmitter and become one more piece of stuff orbiting the sun. The craft will still be listening. But mission managers plan no more calls from home.

"Ulysses has taught us far more than we ever expected about the sun and the way it interacts with the space surrounding it," said Richard Marsden, who has been Ulysses's project scientist and mission manager for ESA, in a statement. One final (Are you sure? Really sure?) bit of praise for a groundbreaking mission.